Re: GNAT "alignment value must be positive"

[marciant@earthlink.net]

On Tuesday, April 7, 2015 at 2:47:01 PM UTC-4, Jeffrey Carter wrote:

<snip> 

> So zero should be allowed in this obsolescent form as well.
> 
> If GNAT is rejecting zero when allowed by these rules
> then it would seem to be a compiler error.

I'm linking that also.  If I do not see any better explanation here then I will write a note to AdaCore.  Also here is a "made up" package that exhibits the issue and the compilation messages that GNAT puts out
(I also did some editing after I pasted to this message and hopefully
did not mess up the code-message correspondence):

package Nonaligned_Type_Definitions is

   type Nonaligned_Record_Component_0 is range -4 .. 4;
   for  Nonaligned_Record_Component_0'size      use 4;
   for  Nonaligned_Record_Component_0'alignment use 0;

   type Nonaligned_Record_Component_2 is range -32768 .. 32767;
   for  Nonaligned_Record_Component_2'size      use 16;
   for  Nonaligned_Record_Component_2'alignment use  0;

   type Nonaligned_Record is
      record
         Component_0a : Nonaligned_Record_Component_0;
         Component_0b : Nonaligned_Record_Component_0;
         Component_2  : Nonaligned_Record_Component_2 range 0..9999;
      end record;
   for Nonaligned_Record use
      record
         at mod 0;
         --  ignoring at 0 range  0 ..  0
         Component_0a at 0 range  1 ..  4;
         --  ignoring at 0 range  5 ..  7
         Component_0b at 0 range  8 .. 11;
         --  ignoring at 0 range 12 .. 15
         Component_2  at 2 range  0 .. 15;
      end record;
   for Nonaligned_Record'size use 32;

end Nonaligned_Type_Definitions;

GNAT output:
Nonaligned_Type_Definitions.ads:5:53: alignment value must be positive
Nonaligned_Type_Definitions.ads:9:54: alignment value must be positive
Nonaligned_Type_Definitions.ads:20:17: alignment value must be positive
gnatmake: "Nonaligned_Type_Definitions.ads" compilation error